1. Technical Field of the Invention
This invention relates generally to portable electronic equipment and more particularly to a multi-function handheld device and a battery-optimized system-on-a-chip used therein.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable (or “handheld”) devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radios, pagers, cellular telephones, computer memory extensions (commonly referred to as a thumb drive), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer, data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
Integrated circuits have enabled the creation of a plethora of handheld devices, however, to be “wired” in today's electronic world, a person needs to posses multiple handheld devices. For example, one may own a cellular telephone for cellular telephone service, a PDA for scheduling, address book, etc., one or more thumb drives for extended memory functionality, an MP3 player for storage and/or playback of digitally recorded music, a radio, etc. Thus, even though a single handheld device may be relatively small, carrying multiple handheld devices on one's person can become quite burdensome.
Further, each handheld device uses a battery (or batteries) to supply power to the circuitry of the device when in operation. As a result, battery lifetime is often an important metric used by customers when selecting a handheld device. Therefore, it is important to minimize power consumption from the battery and thus maximize battery life. There are several techniques used to minimize power consumption including using an alternate power source, when available, to power the handheld device so that the energy stored in the battery is consumed only when an alternate power source is not present. Typically, this use of an alternate power source requires external components and/or reduces efficiency by adding additional components to switch the source of the power to a single dc-dc converter. These consequences are not desirable because they increase system cost and reduce performance. Therefore, the need exists for an integrated circuit that is able to select an alternate power source without impacting the efficiency of the primary dc-dc converter and without requiring external components.
Yet further, many handheld devices include an external memory interface to couple to external memory, such as a memory stick, flash memory, etc. The memory interface typically includes a state machine that is programmed to process the reading to and writing from the external memory in accordance with a standardized memory access protocol. As is known, many external memory devices use a standardized memory access protocol, however, recently some manufacturers have deviating from the standardized memory access protocol. The non-standard external memories offer some advantages over the standardized memories, thus are desirable for use with the handheld devices. However, the memory interface state machine is not capable of processing the memory access requests for non-standard memory. Thus, a handheld device would require multiple state machines to process memory access requests with standard and non-standard memories.
Therefore, a need exists for an integrated circuit that provides multiple functions for handheld devices with optimized power consumption and with a minimal requirement of external components.